Type 2 Diabetes May Damage Thinking Skills: Study

Test performance declined noticeably in just two years

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WEDNESDAY, July 8, 2015 (HealthDay News) -- In as little as two years, people with type 2 diabetes may develop problems with blood flow in the brain, which could lower their thinking and memory skills, a small study suggests.

"Our major finding is we have linked the acceleration of the cognitive decline to impaired blood flow regulation in the brain," said senior study author Dr. Vera Novak, an associate professor of neurology at Harvard Medical School in Boston.

The problem the researchers found was with dilation of the blood vessels, which allows more blood to flow through the brain. Adequate amounts of blood are crucial for thinking skills and other activities.

The researchers found that the higher someone's average blood sugar levels were over the previous several months (a measure called A1C), the worse the problem with blood vessel dilation was, Novak said.

The study was published online July 8 in the journal Neurology. It was funded by the U.S. National Institute on Aging, the American Diabetes Association, the Harvard Clinical and Translational Science Center and the U.S. National Center for Research Resources.

In the study, the researchers evaluated 40 people. Their average age was 66. Nineteen of the study volunteers had type 2 diabetes, and 21 didn't have the blood sugar disease.

In type 2 diabetes, the body doesn't use insulin efficiently and eventually can't make enough insulin to control blood sugar levels, according to the American Diabetes Association (ADA). Insulin is a hormone that's crucial for metabolizing carbohydrates in foods. More than 29 million people in the United States have diabetes, and most of them have type 2 diabetes, the ADA said.

The researchers tested everyone at the start of the study, and again two years later. The volunteers completed thinking and memory tests. They were also given MRI scans to look at blood flow in their brains, and they had blood tests to measure their average blood sugar levels and inflammation.

At the two-year mark, those with type 2 diabetes had less ability to regulate blood flow to the brain when needed and scored lower on the thinking and memory tests.

On one test that looked at learning and memory, the scores of those with diabetes dipped an average of 12 percent, from 46 points to 41. Those without type 2 diabetes stayed at an average of 55 points over the two years.

A decline from 46 to 41 would translate roughly to remembering 10 words on a memory test the first time, and then remembering only 8 or 9 two years later, said Novak. "It's only [in] two years, that's what is concerning."

The higher the inflammation levels, the worse the blood flow regulation, the research team found. That was true even for people who had good control of their diabetes.

Blood flow regulation decreased 65 percent in the people with type 2 diabetes, the researchers found.

Dr. Marc Gordon, chief of neurology at Zucker Hillside Hospital, North Shore Long Island Jewish Health System, Manhasset, said it's not new to suggest type 2 diabetes is linked with inflammation and stress to the cells that can lead to problems in the blood vessels.

"What's new here is they are documenting that the changes in the blood vessel in response to circumstances is what seems to be predicting a decline in cognition," said Gordon, who is also professor of neurology and psychiatry at Hofstra North Shore Long Island Jewish School of Medicine.

In other words, he said, it appears the inability of the blood vessels to respond to various demands is what leads to the thinking problem, although inflammation also plays a role in damaging the blood vessels.

In previous research, Novak found that the brain of a person with diabetes is about five years older, on average, than the brain of someone without the condition. "So essentially, the diabetic brain ages faster," she said.

The researchers added that a study with a larger group of people and done for a longer time is needed to better understand how type 2 diabetes may affect blood flow to the brain.